"There is one large mystery that remains to be solved: How did a black hole of such massive proportions form so early in the universe's history? It's thought that black holes grow by accreting, or absorbing mass from the surrounding environment. Extremely large black holes, such as the one identified by Simcoe and his colleagues, should form over periods much longer than 690 million years.

"If you start with a seed like a big star, and let it grow at the maximum possible rate, and start at the moment of the Big Bang, you could never make something with 800 million solar masses—it's unrealistic," Simcoe says. "So there must be another way that it formed. And how exactly that happens, nobody knows.""